Acoustic droplet ejection has proven useful in a number of applications. Acoustic droplet ejection and some of those applications are described in the following U.S. Pat. Nos. and patent applications (and in their citations): 4,308,547 by Lovelady et al., entitled "LIQUID DROP EMITTER," issued 29 Dec. 1981; 4,697,195 by Quate et al., entitled "NOZZLELESS LIQUID DROPLET EJECTORS," issued 29 Sep. 1987; 4,719,476 by Elrod et al., entitled "SPATIALLY ADDRESSING CAPILLARY WAVE DROPLET EJECTORS AND THE LIKE," issued 12 Jan. 1988; 4,719,480 by Elrod et al., entitled "SPATIAL STABLIZATION OF STANDING CAPILLARY SURFACE WAVES," issued 12 Jan. 1988; 4,748,461 by Elrod, entitled "CAPILLARY WAVE CONTROLLERS FOR NOZZLELESS DROPLET EJECTORS," issued 31 May 1988; 4,751,529 by Elrod et al., entitled "MICROLENSES FOR ACOUSTIC PRINTING," issued 14 Jun. 1988; 4,751,530 by Elrod et al., entitled "ACOUSTIC LENS ARRAYS FOR INK PRINTING," issued 14 Jun. 1988; 4,751,534 by Elrod et al., entitled "PLANARIZED PRINTHEADS FOR ACOUSTIC PRINTING," issued 14 Jun. 1988; 4,959,674 by Khri-Yakub et al., entitled "ACOUSTIC INK PRINTHEAD HAVING REFLECTION COATING FOR IMPROVED INK DROP EJECTION CONTROL," issued 25 Sep. 1990; 5,028,937 by Khuri-Yakub et al., entitled "PERFORATED MEMBRANES FOR LIQUID CONTRONLIN ACOUSTIC INK PRINTING," issued 2 Jul. 1991; 5,041,849 by Quate et al., entitled "MULTI-DISCRETE-PHASE FRESNEL ACOUSTIC LENSES AND THEIR APPLICATION TO ACOUSTIC INK PRINTING," issued 20 Aug. 1991; 5,087,931 by Rawson, entitled "PRESSURE-EQUALIZED INK TRANSPORT SYSTEM FOR ACOUSTIC INK PRINTERS," issued 11 Feb. 1992; 5,111,220 by Hadimioglu et al., entitled "FABRICATION OF INTEGRATED ACOUSTIC INK PRINTHEAD WITH LIQUID LEVEL CONTROL AND DEVICE THEREOF," issued 5 May 1992; 5,121,141 by Hadimioglu et al., entitled "ACOUSTIC INK PRINTHEAD WITH INTEGRATED LIQUID LEVEL CONTROL LAYER," issued 9 Jun. 1992; 5,122,818 by Elrod et al., entitled "ACOUSTIC INK PRINTERS HAVING REDUCED FOCUSING SENSITIVITY," issued 16 Jun. 1992; 5,142,307 by Elrod et al., entitled "VARIABLE ORIFICE CAPILLARY WAVE PRINTER," issued 25 Aug. 1992; and 5,216,451 by Rawson et al., entitled "SURFACE RIPPLE WAVE DIFFUSION IN APERTURED FREE INK SURFACE LEVEL CONTROLLERS FOR ACOUSTIC INK PRINTERS," issued 1 Jun. 1993. U.S. patent application Ser. No. 08/245,322, entitled, "ACOUSTIC FABRICATION OF COLOR FILTERS," filed on 18 May 1994. Each of those patents and patent applications is hereby incorporated by reference.
Some applications of acoustic droplet ejection require an accurate alignment of either the acoustic droplet ejectors or of their various components to other structures. For example, consider the fabrication of liquid crystal display color filter arrays as described in U.S. patent application Ser. No. 08/245,322 entitled, "ACOUSTIC FABRICATION OF COLOR FILTERS," filed on 18 May 1994. The technique taught in that patent application involves acoustically ejecting droplets of color filter material (such as polyimide) onto a substrate using forces created by an ultrasonic transducer driven by an RF voltage. In operation, the acoustic forces pass thorough a base and into an acoustic lens which focuses the acoustic energy into a small focal area which is at, or is very near, the free surface of the material being ejected. Provided the energy of the acoustic beam is sufficiently great and properly focused, a droplet is ejected. By ejecting droplets at the proper locations, a color filter is formed on a color filter substrate. However, when fabricating color filters using acoustic droplet ejection the individual droplets should be placed with an accuracy of about 10 .mu.m. This requires an accurate alignment between the acoustic droplet ejectors and the color filter substrate.
While the above describes acoustic fabrication of color filters, other depositions, such as conformal coatings, chemical and biological agents, and inks may also need to be deposited highly accurately.
While accurate alignments between acoustic droplet ejectors and external structures may be important, it may be even more important to accurately align various internal structures which comprise the acoustic printhead. For example, an acoustic printhead may contain thousands of transducers on the rear surface of a substrate which has thousands of acoustic lenses on its front surface. Successful operation of the acoustic printhead requires that the transducers axially align with the lenses to an accuracy of better than 10 .mu.m. This can be difficult to achieve using standard alignment techniques.
In view of the above, techniques which enable precise alignment of acoustic printheads or of their components with various structures would be useful.